U.S. patent number 7,142,873 [Application Number 11/233,247] was granted by the patent office on 2006-11-28 for system and method for calibration of a wireless network.
This patent grant is currently assigned to Technocom Corporation. Invention is credited to Khaled I. Dessouky, Jun Liu, Justin Paul McNew.
United States Patent |
7,142,873 |
McNew , et al. |
November 28, 2006 |
System and method for calibration of a wireless network
Abstract
In one embodiment, the present invention is a method and system
for calibrating a wireless network including a Mobile Switching
Center (MSC), and a Position Determination Device (PDD). The
wireless network is capable of determining the position of a
handset. The method includes receiving a trigger from the MSC;
sending a position request message to the PDD in response to the
received trigger; receiving a position request response message
from the PDD; continuously sending subsequent position request
messages to the PDD in response to the same received trigger, until
a termination command is received; terminating the sending
subsequent position request messages, when the termination command
is received; and generating output data including network
calibration parameters.
Inventors: |
McNew; Justin Paul (Santa
Monica, CA), Dessouky; Khaled I. (Studio City, CA), Liu;
Jun (Sherman Oaks, CA) |
Assignee: |
Technocom Corporation (Encino,
CA)
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Family
ID: |
31498660 |
Appl.
No.: |
11/233,247 |
Filed: |
September 21, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060019674 A1 |
Jan 26, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10634407 |
Aug 5, 2003 |
6993318 |
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60401164 |
Aug 5, 2002 |
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Current U.S.
Class: |
455/456.1;
455/423; 455/456.6; 455/456.5; 340/539.13 |
Current CPC
Class: |
H04W
24/00 (20130101); H04W 28/18 (20130101); H04W
64/00 (20130101); H04W 88/14 (20130101) |
Current International
Class: |
H04Q
7/20 (20060101) |
Field of
Search: |
;455/404.1-404.2,428,445-446,456.1-456.3,423,435.1,432.1,456
;340/357.1,450,539.13,426.19,993 ;342/357.1,450 ;701/1,213 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Feild; Joseph
Assistant Examiner: Afshar; Kamaran
Attorney, Agent or Firm: Christie, Parker & Hale,
LLP.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application is a continuation of U.S. patent application Ser.
No. 10/634,407, filed Aug. 5, 2003 now U.S. Pat. No. 6,993,318,
which claims the priority of U.S. Provisional Patent Application
No. 60/401,164, filed Aug. 5, 2002. The complete disclosures of
which are incorporated herein by reference.
Claims
What is claimed is:
1. A method for calibrating a wireless network including a position
determination device (PDD), the method comprising: receiving a
voice or data calibration call; establishing a loop process
responsive to the voice or data calibration call; generating and
sending a plurality of position request messages to the PDD within
the loop process; receiving a plurality of position request
responses from the PDD in response to the plurality of position
request messages, within the loop process; receiving a termination
trigger; terminating the loop process and the generating and
sending of the plurality of subsequent position request messages
when the termination trigger is received; and sending a termination
message in response to the received termination trigger.
2. The method of claim 1, further comprising generating output data
for use in network calibration.
3. The method of claim 1, wherein the termination trigger is a
voice or data call termination message from a mobile switching
center.
4. The method of claim 1, wherein the termination trigger is
release of a phone call.
5. The method of claim 1, further comprising generating a feedback
signal.
6. The method of claim 1, further comprising: receiving a voice or
data call; sending a first position request message to the PDD in
response to the received voice or data call; receiving a position
response message from the PDD; and sending a second position
request message to the PDD in response to the same received voice
or data call and the received position response message.
7. A system for calibrating a wireless network including a Position
Determination Device (PDD) comprising: means for receiving a voice
or data calibration call; means for establishing a loop process
responsive to the voice or data calibration call; means for
generating and sending a plurality of position request messages to
the PDD within the loop process; means for receiving a plurality of
position request responses from the PDD within the loop process;
means for receiving a termination trigger; means for terminating
the loop process and the generating and sending of the plurality of
subsequent position request messages when the termination trigger
is received; and means for sending a termination message in
response to the received termination trigger.
8. The system of claim 7, further comprising means for generating
output data for use in network calibration.
9. The system of claim 7, wherein the termination trigger is a
voice or data call termination message from a mobile switching
center.
10. The system of claim 7, wherein the termination trigger is
release of a phone call.
11. The method of claim 7, further comprising generating a feedback
signal.
12. The system of claim 7, further comprising: means for receiving
a voice or data call; means for sending a first position request
message to the PDD in response to the received voice or data call;
means for receiving a position response message from the PDD; and
means for sending a second position request message to the PDD in
response to the same received voice or data call and the received
position response message.
13. A method for calibrating a wireless network including a
position determination device (PDD), the method comprising:
establishing a loop process responsive to a voice or data
calibration call; generating and sending a plurality of position
request messages to the PDD within the loop process; receiving a
plurality of position request responses from the PDD within the
loop process; generating a calibration sample as a difference
between an absolute time reference and an actual time reference for
each received position request response; and aggregating the
calibration samples for the plurality of received position request
responses to generate a calibration value.
14. The method of claim 13, further comprising generating a
termination trigger to terminate the generation and sending of the
plurality of position request messages.
15. The method of claim 14, wherein the termination trigger is a
voice or data call termination message from a mobile switching
center.
16. The method of claim 14, wherein the termination trigger is
release of a phone call.
17. The method of claim 13, further comprising generating a
feedback signal.
18. The method of claim 13, further comprising: receiving a voice
or data call; sending a first position request message to the PDD
in response to the received voice or data call; receiving a
position response message from the PDD; and sending a second
position request message to the PDD in response to the same
received voice or data call and the received position response
message.
Description
FIELD OF THE INVENTION
The present invention relates to a wireless communication network.
More specifically, the present invention relates to a method and
apparatus for generating calibration data for positioning
determination systems in wireless networks.
BACKGROUND OF THE INVENTION
Wireless networks can determine the position of a mobile device
based on trilateration using, for example, time difference
measurements taken by the wireless handset, or by components
installed in the wireless network or adjunct to it.
The challenge of trilateration on wireless signals, e.g., in PCS
and cellular networks, is that those networks have transmitters
and/or receivers that are either unsynchronized or loosely
synchronized to a timing reference that is of insufficient accuracy
to support location via trilateration. This problem can be
corrected by calibrating the wireless network and/or Position
Determination Device to determine these calibration values and in
turn subtract their effects from subsequent position
calculations.
Calibrating a network can be an expensive and time-consuming
process. In order to achieve statistical significance, many
calibration data samples are required. Traditional methods utilize
a substantial amount of test equipment to obtain the necessary
calibration data. A typical method requires the tester to generate
a significant number of calls from a wireless handset. Each call is
received by the Mobile Switching Center, which forwards the call to
another device that accepts the call and issues one Position
Request message per call, generating a single Position Response
Only one calibration sample is generated per Position Response,
therefore many calls are required to generate a sufficient number
of samples. To generate the number of Position Requests required
for statistical significance, the tester must make an equal number
of calls, which is generally time consuming because the tester has
no knowledge of when the Position Response was received by the
device that issued the Position Request. The limiting factor is
that this traditional method generates only one calibration sample
per invocation of the Position Determination process when used for
calibration purposes.
A calibration sample is defined herein as a measurement of the
difference between an absolute time reference, and the actual time
reference being used by the components in the wireless network.
Each reference point in a wireless network can be associated with
an observed time, and the calibration value associated with that
reference point is subtracted from the observed time reference to
achieve a reference closer to absolute time. The calibration value
is comprised of many calibration samples via averaging or other
statistical methods.
SUMMARY OF THE INVENTION
The present invention is a method and system for network assisted
calibration (NAC) in a wireless network. The NAC method and system
cause a Position Determination Device to rapidly generate wireless
network calibration data. This calibration data is generally used
to improve the location accuracy of position determination systems
that rely on trilateration within cellular networks. When
integrated with a wireless intelligent network, the system of the
present invention assumes the role of a messaging system and
wireless call-taking device (landline voice or data network) during
calibration calls that autonomously causes the rapid and efficient
generation of calibration data.
In one embodiment, the present invention is a method and system for
calibrating a wireless network including a Mobile Switching Center
(MSC), and a Position Determination Device (PDD). The PDD within
the wireless network is capable of determining the position of a
handset. The method includes receiving a phone call from the MSC;
sending a first position request message to the PDD responsive to
the received phone call; receiving a position request response
message from the PDD; continuously sending subsequent position
request messages to the PDD corresponding to the same received
phone call; terminating the sending of subsequent position request
messages, when a termination trigger is received from the MSC; and
sending a call termination message to the MSC in response to the
received termination trigger.
In another embodiment, the present invention is a method and system
for causing generation of calibration data in a wireless network
including a Mobile Switching Center (MSC), and a Position
Determination Device (PDD) to determine position of a handset. The
method includes receiving a trigger from the MSC; sending a
position request message to the PDD in response to the received
trigger; receiving a position request response message from the
PDD; continuously sending subsequent position request messages to
the PDD in response to the same received trigger, until a
termination command is received; terminating the sending subsequent
position request messages, when the termination command is
received; and causing the generation of output data for use in
network calibration. The trigger may be generated by a call
origination message from the MSC or by a received call from the
handset. Moreover, the termination command may be a call
termination message from the MSC, or the termination may occur when
the call origination message from the MSC is released.
Still other embodiments of the present invention will become
readily apparent to those skilled in the art from the following
detailed description, wherein is shown and described only
embodiments of the invention by way of illustration of the best
modes contemplated for carrying out the invention. As will be
realized, the invention is capable of other and different
embodiments and its several details are capable of modification in
various obvious respects, all without departing from the spirit and
scope of the present invention. Accordingly, the drawings and
detailed description are to be regarded as illustrative in nature
and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exemplary illustration of position determination in a
wireless network;
FIG. 2 is an exemplary architecture used to enable location
services in a wireless network;
FIG. 3 is a network reference model for a wireless Phase 2 911;
FIG. 4 is an exemplary block diagram of a system for network
assisted calibration, according to one embodiment of the present
invention;
FIG. 5 is an exemplary block diagram of a system, according to
Messaging Only embodiment;
FIG. 6 is an exemplary process flow diagram, according to Messaging
Only embodiment;
FIG. 7 is an exemplary state diagram, according to Messaging Only
embodiment;
FIG. 8 is an exemplary block diagram of a system, according to Call
Path embodiment;
FIG. 9 is an exemplary process flow diagram, according to Call Path
embodiment;
FIG. 10 is an exemplary state diagram, according to Call Path
embodiment;
FIG. 11 is an exemplary block diagram of a system, according to
Hybrid embodiment;
FIG. 12 is an exemplary process flow diagram, according to Hybrid
embodiment;
FIG. 13 is an exemplary state diagram, according to Hybrid
embodiment; and
FIG. 14 is an exemplary log file, according to one embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an exemplary position determination
configuration 100 in a wireless network. The configuration 100
includes wireless sites (or base stations) 102, 104, 106 with known
positions and a wireless handset 114 with an unknown position. Once
the time difference measurements 108, 110 and 112 between the
wireless sites 102, 104, 106 and the wireless handset 114 are
performed, the handset position can be determined by trilateration
from known positions of the wireless sites 102, 104, 106. In
practice, wireless sites within a location determination system
operate according to local timing references. These timing
references may not be exactly the same for each wireless site, and
the resulting offsets cause some amount of error in the location
computation.
Calibration is a process that reduces this position error by
comparing the time reference of each wireless site to a common
reference to account for the timing differences. The calibration
process may utilize the actual measurements used for trilateration
and positioning when the location of the wireless handset is
already known, because the propagation delay between each wireless
site and the handset can be computed based on the respective
location of each. By using these measurements to calibrate the
location determination system, location accuracy can be
significantly improved.
For example, in realization of Phase-2 911 and other location based
services, the network elements typically involve one or more of the
following generic devices: Mobile Switching Center, Mobile Position
Gateway and Position Determination Device. The Mobile Switching
Center is responsible for call routing and managing the setup and
teardown of voice circuits. The Mobile Position Gateway assists the
Mobile Switching Center in determining how to route the call. The
Position Determination Device is responsible for calculating the
position of the mobile handset.
The basic architecture for a wireless network enabled with location
capabilities is illustrated in FIG. 2. In this representation, the
Mobile Switching Center 202 includes the wireless sites (base
stations) connected to it directly or through a base station
controller. The primary responsibility of the Mobile Switching
Center 202 is routing telephone calls to and from the wireline
voice or data network 204. The Mobile Position Gateway 206 manages
location information for wireless handsets, and provides an
interface for external devices including the wireline network 204
to request position information. The Position Determination Device
208 is responsible for calculating the location of a wireless
handset, and communicating the position information to the Mobile
Positioning Gateway 206 for management and distribution of the
location information. These elements are part of the wireless
intelligent network that enables operation of radio and location
services, such as, those utilized in cellular
telecommunications.
One embodiment of such a wireless network is realized in Wireless
Phase-2 911 services, in which emergency callers are located for
the entity that receives the emergency call. This architecture is
illustrated in FIG. 3. As shown, the Mobile Positioning Center
(MPC) 306, and Position Determination Entity (PDE) 308 are
respective embodiments of Mobile Positioning Gateway 206, and
Position Determination Device 208 of FIG. 2. The Emergency Services
Network 304 is one embodiment of the wireline voice and data
network 204 (of FIG. 2). In FIG. 3 the AiDi interface is used to
carry voice conversations over a "call path" between the MSC and
the Emergency Services Network. The E3 interface is used by the MSC
to request call path utilization instructions from the MPC using
"messaging". The E5 interface is used by the MPC to request
position from the PDE, also using messaging. The E12 is a third
messaging interface used for communication between the PDE and a
handset, which is carried through the MSC. The Emergency Services
Network corresponds to a specific application, namely Phase 2 911
services that utilize location to assist emergency callers. When it
receives an emergency call on the AiDi interface, it uses messaging
on the E2 interface to request position from the MPC. For PSC 1900
or GSM and UMTS networks, the Gateway Mobile Positioning Center and
Serving Mobile Location Center act as the Mobile Positioning
Gateway 206 and Position Determination Device 208,
respectively.
When a call that requires location identification is initiated on a
wireless network, such as for Phase-2 911 services, intelligent
network messages are exchanged between network devices over
signaling interfaces to instantiate call setup procedures. When a
call is placed to a facility that requires location capabilities,
certain embodiments of these messages are exchanged to request and
respond with the calculated location of the wireless handset. The
messages of interest in this case are termed generically: Call
Origination messages, Call Termination messages, and Position
messages. These messages can be of either a Request or Response
variety.
Call Origination Request messages are typically exchanged between
the Mobile Switching Center 202 and other network devices. They are
used to notify other network elements that a call is being setup
and to request services to assist in this task. Call Termination
messages are exchanged between the Mobile Switching Center 202 and
other network devices. They are used to notify other network
elements that a call has terminated and resources associated with
this call can be released.
Position messages are exchanged between the Mobile Position Gateway
202 and the Position Determination Device 208. They are used to
request and respond with the calculated position of a handset.
Position messages are also exchanged between the Mobile Position
Gateway 206 and the wireline voice and data networks 204 (e.g. an
Emergency Services Network 304 in FIG. 3) tasked with retrieving
caller location. These messages are also used to request updates of
a handset's position.
When the Position Determination Device has been implemented within
a wireless network, the wireless network infrastructure and
handsets support some form of trilateration, wherein the position
of the handset is also determined through another independent
process, for example, Global Positioning System (GPS). In one
embodiment, in order to trigger the NAC process, a calibration call
is placed from a wireless handset to a standard telephone or to the
NAC system. The NAC system described herein assumes the
responsibility of the Mobile Position Gateway and in certain
embodiments the wireline voice or data network for calibration
calls. More importantly, the system enables the rapid generation of
calibration data as described in the paragraphs that follow.
One of the differences between the present invention and the Mobile
Position Gateway is that the present invention enters a "loop"
process whereby it autonomously generates multiple position request
messages to the Position Determination Device per calibration call.
However, for normal calls, the Mobile Position Gateway is only
permitted to generate a single position request message per call
and does not have any call interface. Another difference between
the present invention and the Mobile Position Gateway is that the
present invention also acts as a call-taking device. The processes
of this call-taking device (as explained later) closely coupled
with the NAC's messaging engine effect the rapid generation of data
required for calibration.
FIG. 4 is an exemplary block diagram of a NAC system, according to
one embodiment of the present invention. As shown, there are two
interfaces: the Call Interface 402 used for handling voice or data
calls forwarded from the handset 114 through the Mobile Switching
Center 202, and the Message Interface 404 used for handling
messages to and from the Mobile Switching Center 202 and the
Position Determination Device 208. The interface between the Mobile
Switching Center 202 or the Position Determination Device 208 and
the handset 114 are outside the scope of this embodiment of the NAC
system. The NAC system 400 also includes two core elements, the
Call Processing engine 406 and the Message Processing engine 408.
The Call Processing engine 406 accepts voice or data calls and
provides voice or data status information to the handset over the
corresponding voice or data interface, for example, synthesized
speech or text messages. The Mobile Position Gateway is neither
equipped with this capability, nor intended for use in such a
manner in a wireless network. The Message Processing engine 408
handles the sending and receiving of Call Origination/Termination
Request, Call Origination/Termination Response, Position Request
and Position Response messages. The Call Processing and the Message
Processing engines may communicate on an internal interface to
facilitate the NAC process, for example, to detect that a
calibration call has ended. The interface between these engines
also makes use of the Call Origination/Termination Request and
Response messages.
There are different ways to initiate/terminate the NAC process
based on the calibration calls or Message exchanges, including but
not limited to:
A Messaging Only Method: With the Messaging Only method, the NAC
process is triggered and terminated via the Message Interface 404
by Call Origination/Termination messages from a Mobile Switching
Center. The details are described below with reference to FIGS. 5,
6 and 7.
A Call Path Method: With the Call Path method, a calibration call
is made directly to the NAC system (forwarded from the Mobile
Switching Center). The NAC process is triggered and terminated via
the Call Path Interface 402. The details are described below with
reference to FIGS. 8, 9 and 10.
A Hybrid Method: With the Hybrid method, the NAC process is
triggered via the Message Interface 404 but terminated via the Call
Path Interface 402. The details are described below with reference
to FIGS. 11, 12 and 13.
After the NAC process is triggered, the NAC system 400 begins
sending multiple Position Request messages in rapid sequence to the
Position Determination Device 208. After sending a Position Request
message to the Position Determination Device, the NAC system waits
for a response message. When the system receives a Position
Response message, it logs the message and immediately sends another
Position Request message. This process may be implemented
sequentially using a single calibration call by a single handset.
Alternatively, more than one calibration calls made by a plurality
of handsets may be processed in parallel. Position Messages are
always sent on the Message Interface 404 between the NAC system 400
and the Position Determination Device 208, regardless of the method
used to trigger/terminate the process. The processing within the
NAC system may be stopped after generation of a sufficient amount
of samples. Alternatively, the process may continue indefinitely or
until the call is terminated.
The NAC system 400 makes a plurality of Position Determination
Requests for each Call Origination Request. The system allows a
substantial number of Position Requests to be generated for
statistical significance while only requiring the tester to make a
single call. This speeds up the process significantly and saves
time.
The system also has accurate knowledge of when the Position
Determination Device 208 has completed its position computations
through having received the Position Response message (the Position
Response message is generated by the Position Determination Device
208 when it has completed its position computations), therefore,
minimizing the amount of time between subsequent requests. This
eliminates significant uncertainty on the part of a tester who is
making calibration calls, wherein the tester does not have specific
information about the time it takes to make a location fix by the
Position Determination Device 208. When the call path interface is
utilized during a calibration call the NAC system can provide
immediate feedback as to the status of messages via audible
mechanisms inherent to the handset 114, for example, synthesized
audio.
In one embodiment, the NAC system 400 terminates the Position
Request generation process when the calibration call is ended,
which overcomes a significant challenge wherein Position Request
messages would continue to be generated after a calibration call
has ended or the handset is no longer available. The NAC process
may also be terminated after a specified number of requests have
been made.
For the Messaging Only method, as shown in FIG. 5, the NAC system
400 includes the Message Interface 404 and Message Processing
engine 408. The Call Path Interface 402 and Call Processing engine
406 are not required in this embodiment. The Mobile Switching
Center 202 sends a Call Origination Request message to the NAC
system 400. Then the NAC system returns a Call Origination Response
message to the Mobile Switching Center 202 on the same messaging
interface so that the call can be forwarded to the wireline voice
or data network. The NAC process is subsequently triggered. The NAC
process may be stopped after generation of a sufficient amount of
samples, or the process may continue until a Call Termination
Request message is received from the Mobile Switching Center
202.
FIG. 6 presents a process flow chart based on the Messaging Only
method. The process begins with block 602 where the NAC system 400
waits for a Call Origination Request message from the Mobile
Switching Center 202. In block 604, the NAC system determines if a
Call Origination Request has been received. If not, the process
goes back to block 602 and waits. If the Call Origination Request
has been received, in block 606, the NAC system 400 sends a Call
Origination Response to the Mobile Switching Center 202 (so that
the Mobile Switching Center can forward the call to its
destination). Then in block 608, the NAC system 400 sends a
Position Request to the Position Determination Device 208. This
causes the Position Determine Device 208 to generate the necessary
information and calculate the position of the handset 114 that
placed the call.
Upon successful completion of position calculation, the Position
Determination Device 208 sends a Position Response message back to
the NAC system 400. In block 610, the NAC system waits for the
Position Response message from the Position Determination Device
208 or a Call Termination request message from the Mobile Switching
Center 202. After the NAC system 400 receives a Position Response
message in block 612, the process goes back to block 608 and sends
another Position Request. Finally, after the NAC system 400
receives a Call Termination Request message from the Mobile
Switching Center 202 in block 614 indicating that the test is
complete, the process stops.
FIG. 7 presents the corresponding state machine. The start state
702 is to wait for a Call Origination Request message from the
Mobile Switching Center 202. When a call is placed from a cellular
handset 114, the Mobile Switching Center 202 sends a Call
Origination Request message to the NAC system 400.
The next state 704 is to send a Call Origination Response message
back to the Mobile Switching Center 202 for the call to be quickly
forwarded to the destination . The next state 706 is to send a
Position Request message to the Position Determination Device 208.
This message causes the Position Determination Device 208 to
calculate the position of the cellular handset 114 that placed the
call.
The next state 708 is to wait for either a Position Response
message from the Position Determination Device 208 or a Call
Termination message from the Mobile Switching Center 202. A
Position Response message is sent by the Position Determination
Device 208 when it has finished calculating the position of the
cellular handset 114 and contains the calculated position. If this
message is received then go to state 706. Alternatively, a Call
Termination Request message is sent by the Mobile Switching Center
202 when the call is terminated.
The final state 710 is to send a Call Termination Response message
back to the Mobile Switching Center 202. This confirms that the
activity associated with this call has been concluded. This is
followed by a return to the start state 702.
For the Call Path method, as shown in FIG. 8, the NAC system 400
uses Call Path Interface 402 to communicate with the Mobile
Switching Center 202, and uses Message Interface to communicate
with the Position Determination Device 208. In this embodiment, a
calibration call is made directly to the NAC system 400 from the
Mobile Switching Center 202; it is received by the Call Processing
Engine. The Call Processing engine 406 handles the received signal
and sends a Call Origination message to the Messaging Processing
engine, as is done between the MSC and the NAC system for the
Messaging Only method. This triggers the NAC process. The NAC
process may be stopped after generation of a sufficient amount of
samples. Alternatively, the process may continue until the Call
Processing engine 406 generates a Call Termination message to the
Messaging Processing engine 408 as the call is released or
terminated (the calibration call is ended by the tester)
FIG. 9 presents a process flow chart based on the Call Path method.
As shown, the process begins with block 902 where the NAC system
400 waits for a calibration call. Upon the receipt of a calibration
call, the Call Processing engine 406 generates a Call Origination
message within block 904. Then in block 608, the NAC system 400
sends a Position Request to the Position Determination Device 208.
This causes the Position Determination Device 208 to gather the
necessary information and calculate the position of the handset 114
that placed the call.
When the position calculation is successfully completed, the
Position Determination Device 208 sends a Position Response message
back to the NAC system 400. In block 910, the NAC system waits for
the Position Response message from the Position Determination
Device 208, or call termination or release of the Call Path
Interface (indicating the calibration call is ended, whereby the
Call Path corresponding to the calibration call is released by the
Mobile Switching Center 202). In the latter case, the system
monitors the call path from the MSC and determines when that call
path is released by the MSC. After the NAC system 400 receives a
Position Response message in block 612, the process goes back to
block 608 and sends another Position Request. Block 914 checks if
the call to NAC system is terminated. Upon the call termination in
block 916, the Call Processing engine generates a Call Termination
message to the Message Processing engine. This indicates that the
test is completed and the process stops.
FIG. 10 presents the corresponding state machine. The start state
1002 is to wait for a calibration call forwarded from the Mobile
Switching Center 202 to the NAC system 400. The next state 1004 is
to process the received signal and generate a Call Origination
message by the Call Processing engine 406. The Call Origination
message is sent to the Messaging Processing Engine 408 via an
internal interface, and this triggers the NAC process.
The next state 706 is to send a Position Request message to the
Position Determination Device 208. This message causes the Position
Determination Device 208 to calculate the position of the cellular
handset 114 that placed the call. The next state 1008 is to wait
for either a Position Response message from the Position
Determination Device 208 or the Call to NAC terminated. A Position
Response message is sent by the Position Determination Device 208
when it has finished calculating the position of the cellular
handset 114 and contains the calculated position. When this message
is received, then go to state 706. When, a call termination or
release of the Call Path Interface occurs, then go to the final
state 1010.
The final state 1010 is to generate a Call Termination message by
the Call Processing engine 406 upon call termination. The Call
Termination message is sent to the Message Processing engine 408
via an internal interface. This concludes the NAC process and the
process returns to the start state 1002.
For the Hybrid method, as shown in FIG. 11, the NAC system 400 uses
both the Call Path Interface 402 and the Message Interface 404 to
communicate with the Mobile Switching Center 202, and also uses the
Message Interface to communicate with the Position Determination
Device 208. In this embodiment, when a call is placed from a
handset 114 to the NAC system, the Mobile Switching Center 202
sends a Call Origination Request message to the NAC system 400.
Then the NAC system returns a Call Origination Response message to
the Mobile Switching Center, and this message contains information
that causes the Mobile Switching Center to also route the call to
the NAC system. The NAC process is subsequently triggered. The NAC
process may be stopped after generation of a sufficient amount of
samples, or the process may continue until the Call Processing
engine 406 generates a Call Termination message to the Message
Processing engine 408 as the call to NAC is released or
terminated.
FIG. 12 depicts a process flow chart based on the Hybrid method.
The process begins with block 602 where the NAC system 400 waits
for a Call Origination Request message from the Mobile Switching
Center 202. In block 604, the NAC system determines if a Call
Origination Request has been received. If not, the process goes
back to block 602. If a Call Origination Request has been received,
the process goes to block 1206 where the system sends a Call
Origination Response to the Mobile Switching Center 202 (and this
response message causes the Mobile Switching Center 202 to also
forward the call to the NAC system's Call interface 402. Then in
block 608, the NAC system 400 sends a Position Request to the
Position Determination Device 208. This causes the Position
Determination Device 208 to gather the necessary information and
calculate the position of the handset 114 that placed the call.
When the position calculation is successfully completed, the
Position Determination Device 208 sends a Position Response message
back to the NAC system 400. In block 910, the NAC system waits for
the Position Response message from the Position Determination
Device 208, or call termination or release of the Call Path
Interface from the Mobile Switching Center 202. After the NAC
system 400 receives a Position Response message in block 612, the
process goes back to block 608 and sends another Position Request.
In Block 914, the process checks if the call to NAC is terminated.
Upon call termination (the tester has ended the call, and the Call
interface is released) in block 916, the Call Processing engine
generates a Call Termination message to the Message Processing
engine indicating that the test is complete, and the process
stops.
FIG. 13 presents the corresponding state machine. As shown, the
start state 702 is to wait for a Call Origination Request message
from the Mobile Switching Center 202. When a call is placed from a
cellular handset 114 to the NAC system 400, the Mobile Switching
Center 202 sends a Call Origination Request message to the NAC
system 400.
The next state 1304 is to send a Call Origination Response message
back to the Mobile Switching Center 202. This response message
contains the information that requires the Mobile Switching Center
202 to also route the call to the NAC system 400. The next state
706 is to send a Position Request message to the Position
Determination Device 208. This message causes the Position
Determination Device 208 to calculate the position of the cellular
handset 114 that placed the call.
The next state 1008 is to wait for either a Position Response
message from the Position Determination Device 208 or the call to
NAC terminated. A Position Response message is sent by the Position
Determination Device 208 when it has finished calculating the
position of the cellular handset 114 and contains the calculated
position. If this message is received then go to state 706.
Alternatively, a call termination or release of the Call Path
Interface leads to the final state 1010.
The final state 1010 is to generate a Call Termination message by
the Call Processing engine 406 upon call to NAC termination. The
Call Termination message is sent to the Message Processing engine
408 via an internal interface. This concludes the NAC process and
the process returns to the start state 702.
The result of the NAC process is a log file generated by the
Position Determination Device that contains a significant number of
calibration samples generated over a certain time period, which is
significantly more than the number of calibration samples that can
be generated without a NAC system over the same time period. These
calibration samples are used externally to the NAC system in order
to determine the calibration values as described in the background
of the invention. The key to generating significantly more
calibration samples than is possible without NAC is the plurality
of Position Request messages that is generated per call (the number
of messages that can be generated per call is not bounded).
Furthermore, the fact that the NAC process recognizes when each
location is completed significantly reduces the time required to
obtain a single sample, thus resulting in a significant time
savings as compared to methods subject to uncertainty of processing
time required by the Position Determination Device.
When the call path method or hybrid method embodiments described
herein are used, the audible feedback mechanisms to the handset,
and hence the tester, are also enabled via the triggers used to
start the NAC process. In this case, the handset is provided with a
synthesized speech generated by the NAC system, which entails
notifying the tester of the progress of the NAC process. For
example, the tester hears "sample 1 complete, calibration call
location is <Latitude and Longitude of location of the
calibration sample 1>; sample 2 complete calibration call
location is <Latitude and Longitude of location of the
calibration sample 2>; etc. This audible feedback mechanism
continues throughout the duration of the calibration call. The
location associated with a calibration sample is generated from the
log file, which is output from the NAC system. An example of this
log file is shown in FIG. 14.
In one embodiment, the log file is generated from the Position
Request and Position Response messages. The Position Request
Message contains a telephone number that identifies the handset
that made the calibration call, which is used by the Position
Determination Device 208 to locate the correct handset. The
Position Response Message sent in response to the Position Request
message contains the latitude and longitude of the handset for that
calibration sample. This facilitates synthesizing the speech that
provides the audible feedback to the handset/tester. A log file
entry is created for each handset used to make calibration
calls.
It will be recognized by those skilled in the art that various
modifications may be made to the illustrated and other embodiments
of the invention described above, without departing from the broad
inventive scope thereof. It will be understood therefore that the
invention is not limited to the particular embodiments or
arrangements disclosed, but is rather intended to cover any
changes, adaptations or modifications which are within the scope
and spirit of the invention as defined by the appended claims.
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